When a sample is repeatedly irradiated with intense excitation light intermittently but for a relatively long time, as in time-lapse fluorescence observation of a sample using a microscope, a known microscope measures the cumulative time over which the excitation light is radiated, and, when the cumulative time exceeds a predetermined reference value, issues a notification to that effect or shuts off the excitation light for the purpose of reducing invasion of the sample with the excitation light (for example, see Japanese Unexamined Patent Application, Publication No. 2005-331889).